FIG. 15 is a view showing a basic configuration of the most general ultrasonic wave measuring apparatus of the conventional art. The following description describes features in analyzing an ultrasonic reflected signal, but the basic method, aim, and solution are the same for systems using other means such as a transmission method.
As shown in FIG. 15, the ultrasonic wave measuring apparatus is configured by an ultrasonic probe 101, a control unit 104, and an input section 106, where an observed object (object to be observed) 102 is irradiated with an ultrasonic wave generated from the ultrasonic probe 101 with water 103 as a medium, the wave reflected from the observed object 102 is received by the ultrasonic probe 101, and waveform processing, image processing, and the like are performed in the control unit 104 based on information received by the ultrasonic probe 101 to determine quality of an interface and image the determination result. The ultrasonic probe 101 is used for both transmission and reception, and the control unit 104 includes a pulsar receiver for converting the ultrasonic wave received by the ultrasonic probe 101 to voltage and amplifying the same, and an image processing unit for imaging an intensity value of an observed waveform 105. An electronic package such as a semiconductor chip is assumed as a specific example of the observed object 102. The ultrasonic wave transmits even through the interior of the observed object 102, and the reflected wave generates even from the interior interface. Therefore, the signal received by the ultrasonic probe 101 has a waveform in which plural waves generated from plural interfaces are overlapping.
An example of the reflected waveform is shown in FIG. 16. Specific examples of the observed object serving as an object to be detected include an electronic package mounted on a board. An example for a case where the electronic package, which is a specific example of such an observed object, is submerged under water is shown in FIG. 17A. As shown in FIG. 17A, an electronic package 29, which is a specific example of the observed object, placed in liquid (water) 27 has a plurality of interfaces (e.g., respective contacting surfaces of a semiconductor chip 22, an interposer layer 23, a solder bump 24, a mother board 25, and the like), and thus a plurality of reflected waves 26 is reflected from the electronic package 29 when the electronic package 29 is irradiated with the ultrasonic wave. Such reflected waves 26 are outputted in a form where the plurality of reflected waves are combined, as shown in FIG. 16.
Another example of the detected object is shown in FIG. 18. In this example, an observed object 29A has a single structure, and does not have a plurality of boundary surfaces in the inner portion of the observed object as with the observed object 29 of FIG. 17A, where the reflected wave 26A of the ultrasonic wave is assumed to generate from two locations, the interface between water and the surface of the observed object 29A and the interface between a bottom surface of the observed object 29A and a bottom surface of a water tank. Thus, even if the observed object 29A does not have plural boundary surfaces, the reflecting interface of the ultrasonic wave always exists in plurals, and thus the reflected wave also exists in plurals, whereby a form in which the plurality of reflected waves are combined as in FIG. 16 is obtained.
An ultrasonic wave measuring method of making quality determination on the interface of the observed object with the ultrasonic wave measuring apparatus of the conventional art will be described with reference to FIG. 16. In the conventional art, a trigger 11 is first applied on a surface wave from which an ultrasonic waveform is stably generated. Then, the setting of a time region referred to as gate 12 is performed with the trigger 11 as a zero base point. The gate region needs to contain information of the interface to be observed. In other words, the reflected wave containing information on the interface to be measured is selected from the combined wave of the plurality of reflected waves generated due to the presence of a plurality of interfaces, and the gate 12 is set in the relevant time region. In addition to the gate position, the set value of the gate 12 includes gate width or number of gates.
The gate width is normally set to the reflected wave width of a time slot to be focused, and in most cases, set to a length of one cycle of a sinusoidal wave or shorter. The frequency band of the ultrasonic wave used in the electronic package is between about 10 and 100 MHz, and thus the gate width is often set between 10 and 100 ns. The number of gates is set in plurals to compare with other gate information when the information of the interface to be measured is unknown. Quality determination of the observed object 102 is performed mainly with the waveform intensity value within the interval of the gate 12 set in the above manner. The determination method includes determination using a maximum value and a minimum value (negative maximum value), the maximum value of the absolute value, or the like of the waveform intensity within the interval of the gate 12.    Patent document 1: Unexamined Japanese Patent Publication No. 5-333007    Patent document 2: Unexamined Japanese Patent Publication No 6-294779